The invention relates to osteosynthetic fixation and force transmitting apparatus. More particularly, the invention relates to improvements in apparatus of the type wherein two or more force transmitting members which are movably connected to each other can be directly or indirectly affixed to bones, bone fragments or auxiliary osteosynthetic parts.
Osteosynthesis of tubular bones following fractures or corrective osteotomy invariably or often necessitates the positioning of bones or bone fragments in a predetermined position and/or orientation and subsequent immobilization of the properly positioned and/or oriented bones or bone fragments against any movement until the mending or healing process has progressed sufficiently to warrant removal of the apparatus. The problem of proper fixation of bone fragments and interfragmentary fragment compression is recognized for many years, and many proposals to solve such problem are known in the art. On the other hand, much less attention was devoted to the equally important task of moving the bones and bone fragments to an optimum position or orientation relative to each other.
The task of properly positioning and orienting bones and bone fragments is assigned to osteopaths and other specialists in the bone mending and bone setting field. Thus, it is left to the skill and dexterity of the specialist to properly position and orient the bones or bone fragments in the body of a patient without any, or without adequate, equipment to assist the specialist in the performance of such tasks. Therefore, the results of operations which involve resetting and/or reorienting of bones or bone fragments are often quite unsatisfactory. Moreover, the absence of adequate equipment to assist the specialist necessitate long-lasting operations, incomplete or unsatisfactory repositions following bone fractures and improper orientation of the axes of various mended joints. Improper orientation of the axis of a joint often entails posttraumatic damage to the joint as a result of incongruity of components of the affected joint and/or local overstressing of the cartilage.
Heretofore, a correction of mutual positions of bone fragments was possible only with assistance from external tensioning systems which are designed to permit correction of the position of the axis of a joint subsequent to initial setting by relying on reposition of bone fragments by way of distraction. A drawback of such tensioning systems is that they necessitate external fixation, i.e., the skin must be traversed by threaded bone pins, bone screws or other parts which are driven into bones or bone fragments. This often causes infections at the loci of penetration of fasteners through the skin. Therefore, many health authorities prohibit prolonged external fixation and restrict such mode of fixation only to primary treatments of seriously injured patients for a limited number of days.
Force transmitting apparatus for osteosynthetic purposes are described and shown, by way of example, in German Pats. Nos. 27 08 866 and 29 38 202 and in European Pat. No. B 02 33 930.
European Pat. No. B 0 073 455 discloses a force transmitting apparatus which constitutes a repositional instrumentality for use in internal osteosynthesis. The patented apparatus renders it possible to perform controlled distraction of bone fragments to thus establish the necessary circumstances for correction, namely to overcome the tensioning of soft parts. The patented apparatus is further capable of correcting or compensating for lateral shifting of bone fragments. However, the patented apparatus also exhibits a number of drawbacks. Thus, correction of, or compensation for, lateral shifting of bone fragments can be achieved only by driving the repositioning screw into the soft tissue at the opposite side of the plate. This can result in injuries to blood vessels and nerves.
An important prerequisite for proper repositioning of fractured bones, especially spinal columns but also in connection with corrective osteotomy, is to ensure the carrying out of accurately metered and controlled angular corrections. Such requirements cannot be met by resorting to heretofore known apparatus including the apparatus of European Pat. No. B 0 073 455. Fixation on the osteosynthetic plate has contributed significantly to simplification of osteotomy involving a lengthening of the bones. However, such fixation interferes with bending of the plate which is often necessary for better conformance to the anatomy of a patient.
Corrective treatment involving elimination or reduction of deformities of the spinal column and/or mending of fractured vertebrae preferably involves a first step of correcting the positions and orientation of bone fragments or bone portions prior to fixation to the plate. Such procedure is complex and difficult, mainly due to special anatomical circumstances, i.e., the available space for the application of screws is minimal because the specialist must be concerned with the position of the spinal cord and, therefore, it is possible to use only one bone screw per vertebra. Furthermore, drilling of holes and introduction of the shanks of bone screws into vertebrae through an already applied plate (such as is known from osteosynthesis of extremities) is difficult or impossible because the specialist in charge is likely to damage the spinal cord due to lack of adequate overview of anatomical circumstances in connection with such types of operations. The situation is analogous in connection with complex corrective osteotomies of extremities, particularly in close or immediate proximity to the joints, i.e., it is desirable and advantageous to ensure that a different setting can be inspected and tested without it being necessary to rely on plate fixation. Thus, it is much simpler to inspect the results of the operation and to carry out, if necessary, the required corrective measures. For example, it is possible to carry out such work without transferring bone screws which invariably constitutes a complex, difficult and time-consuming task.